Sintered moldings are used in many applications, in particular, in automobile construction and there especially as moldings in the engine and also in the transmission. One difficulty in the production of sintered moldings consists in, among other things, producing these with the highest possible density. A molding pressed in one or more steps by a typical powder metallurgical method from a sinterable powder, generally designated as a green compact, is here sintered in a second step under a protective atmosphere, so that a solid and also dimensionally accurate molding is produced.
The density of sintered moldings obtained in such a way depends essentially on the density of the green compact achieved in the first pressing step, the so-called green density (also called pressing density). Therefore it is worth the effort to have green compacts that already feature the highest possible density after just the first pressing step.
The high molding pressures typically used in the state of the art for producing green compacts with a high density, however, result, on one hand, in high wear of the compression molding die itself and also lead, on the other hand, to increased ejection sliding friction of the completed green compact in the extrusion die. In this way, higher ejection forces with correspondingly increased wear are to be applied to the compression molding die. In addition, high ejection forces raise the risk of undesired local redensification and crack formation in the green compact.
From DE 102 44 486 A1, a pressing aid is known that comprises 20 to 60 wt. % of a polyglycol with respect to the total amount of pressing aid and 40 to 75 wt. % of a montan wax with respect to the total amount of pressing aid. In this way it is possible, at pressures of 800 MPa, to produce green compacts that have a pressing density of at least 7.14 g/cm3.
The task of the present invention is to make available a mixture for producing sintered moldings by means of which the previously mentioned disadvantages are avoided.